Adapt spatial transformation matrix for 0-based indices.
See also
sm0to1 for the inverse operation
Other header coordinate space:
mghheader.is.ras.valid(),
mghheader.ras2vox(),
mghheader.ras2vox.tkreg(),
mghheader.scanner2tkreg(),
mghheader.tkreg2scanner(),
mghheader.vox2ras(),
mghheader.vox2ras.tkreg(),
read.fs.transform(),
read.fs.transform.dat(),
read.fs.transform.lta(),
read.fs.transform.xfm(),
sm0to1()